A 40 mile run isn’t much to get heat in to burn off protective coatings, etc. Did you use some sort of exhaust paste on the joins? That could be the culprit until it hardens off. I would give it some time and mileage to see if it settles down.

Doug
2011 Plus 4 in Rich Maroon

1972 750 “ComDom” sprinter
1958 Triton 650
1992 Triumph Trophy 900